how to: adjustment of exposure meter of FTb

<p>Hello.</p>

<p>I just finished aligning the meter rack and the sector gear on my FTb. However, even though this has put right the red flag "out of metering range" adjustment, it has disturbed the exposure meter and I need to adjust that in turn now.</p>

<p>I know that the meter is to be adjusted with the two right hand side variable resistors (pots) located on the left hand side of the viewfinder (while looking at the viewfinder). But I am not sure exactly how to go about doing this. What is the algorithm to follow? I don't have a light meter, but I do have a few cameras whose meters work properly (they also have partial metering), so I do have trusted references. Also, what is the significance of these two variable resistors for exposure metering?</p>

<p>Thanks.</p>

<p>Okay, with the help of google and many online references, I sorted out the meter adjustment.<br>

The two variable resistors beside the viewfinder are the ones that need tweaking.<br /> <br /> The meter is adjusted at three settings.<br /> <br /> - Zero setting is done at 1/4s at ASA 100. At this position, the needle must rest at the lower black warning mark. It should be more or less parallel with the slant of the mark (i.e. pointing at around 8'o clock position).<br /> <br /> - Medium light adjustment is done with the right most var. resistor (the one beside the viewfinder).<br /> <br /> - Bright light adjustment is done with the next one (middle one of the three).<br /> <br /> Rotating the contact point of the variable resistors in the clockwise direction results in larger deflection of the needle, thus requiring smaller aperture setting for proper exposure. For example, if one's FTb is over-exposing (i.e. smaller deflection of the needle, resulting in larger aperture setting) in bright light, one should rotate the middle variable resistor clockwise a bit. This would result in larger deflection, hence a setting of a smaller aperture would be required.<br /> <br /> The reference meter I used for calibration was an EOS 5 set in partial metering mode.<br /> <br /> Here is a picture to illustrate the method.<br /></p><div></div>

<p>HS, You're an engineer to the bone, no doubt.<br>

Most advice given is, don't try it, send it to a professional, you'll just make a shelf trophy out of it. That certainly applies to many people but not everyone. I'm an automation/process control tech so camera guts are like instrumentation to me. I've fixed a few cameras, lenses and some other camera stuff. I know what I'm willing to risk based on how much it cost me, how rare, pretty, mint or just how much it means to me.<br>

I've sent cameras for CLA that exceeded my self set risk level, mint black FTb, mint EF and a very nice T90. I won't open the innards of a zoom but the front element, mount or aperture is fair game but not the aperture of an auto focus lens.<br>

I'll dig into a fixed focal length manual focus lenses but no more than the front element of an auto focus lens. I've learned a few things the hard way but the $10 lens was was within my risk level. Here's the first four things I learned the hard way (camera related).<br>

Never take the three screws out of the side of the mount around the lever section of an FD lens. There is at least 23,000 steel micro balls inside and they are dying to come out. I found about 22,995 of them on the floor and put them back in with tweezers, one at a time. (well maybe it was less than 22,000)<br>

Never take the aperture assembly out without marking exactly where the screws are in the adjustment slots or guaging each aperture stop with drill bit shanks so you can get the aperture opening calibration set as found.<br>

Never unscrew the focus helical completely unless you mark or identify how it goes back or else be prepared for trial and error and adjusting the infinity stop while on a camera body.<br>

Never waste a perfectly good FL or FD lens by removing the mount, disassembling, chucking it in a lathe and cutting .020" off and putting an EOS mount on it. It's fun for about 50 shots then you realize it's a pain in the ass to focus and no more fun. Now it will never work on an FD camera again and it takes up space in the EOS bag. Lenses on adapters are different, it's not permanent so you can revert to their intended use. The're still a PIA to focus without a MF focus screen.</p>

<p>I enjoy tinkering with this stuff and I can tell you do too.</p>

<p>All jobs have their risk level, as Dirty Harry (Clint Eastwood) said, "you've got to ask yourself one question.....Do [you] feel lucky? Well....do ya punk?"</p>

<p>Tim, thanks for the interesting post :)</p>

<p>Completely agree with your risk assessment approach.</p>

<p> </p>

<p>Thank you so much for putting this invaluable post up! I just got my FTb back from the repair shop after an expensive overhaul of the shutter speeds and meter was all messed up. I took it back, he said something had slipped, and said it was fixed, and it wasn't. Maybe he should read this post. I lost confidence in him and decided to take matters in my own hands, and the information here (and your other post on Classic Camera Repair) is just what I needed.<br>

I'm guessing my through the actual work, but what comprises Medium Light as opposed to Bright Light? and what's the third pot for? While I can get the reading from the FTb to match my A1 in some situation, I can't get it to match in another. Is tweaking the two pots back in and forth the way to go? Or is there some better system?</p>

<p>Thanks.</p>

<p>Well I answered my own question with some help from Google: Bright Light is one that gives an EV of 15 (ISO 100), meter set at 1/500 and f8. I hung a normal 60 Watt bulb up in my darkroom and pointed it at the 50mm lens of the camera from a distance that filled the view finder. A tripod that uses mounting shoes served me well here as I was able to mount the A1 and the FTb in the same exact way to compare them. Low light was a piece of off white card stock hung in front of the light that gave a reading of 1/15 at f4 (EV 8). I set the two pots on the FTb to match high and low readings from the A1. Now both cameras read the same way, +/- 1/3 stop, the A1 seems to defer to the wider aperture when the reading is too close to call. The FTb is not that sophisticated, and in low light the needle takes its time drifting into final position.<br>

For those who are interested, look at this: http://books.google.com/books?id=FG4Kas5kO5wC&source=gbs_navlinks_s</p>

<p>Elias, just saw your post. I see that you got it working. I just wanted to add a few things I learned along the way.</p>

<p>Using a diffused light source is important. I tried with a lamp as you did, but consistent results were obtained by defusing it. I used a 100 W lamp in a desktop lamp, covered the opening of the lamp share with a typical letter size laser printer page, and coincidentally got a 15ev light source! I measure the light using two cameras such that the backlit paper sheet filled the screen (50mm f/1.8 lens). Be careful with the time, you don't work to burn that sheet from the heat of a 100 W bulb!</p>

<p>Also, bright light source is 15ev: should give f=5.6 at t=1/1000, ISO speed 100.<br>

Medium light source: 10ev. Should give f=5.6 at t=1/30, ISO speed 100. Usually use part of a wall of a room that gives me similar exposure from a known good meter or a camera.<br>

Low light source: 4ev. Should give f=1.4 at t=1/8 (or f=2 at t=1/16), , ISO speed 100. Usually use part of a wall of a room that gives me similar exposure from a known good meter or a camera.</p>

<p>BTW, perhaps it will be a good idea to use the reference camera in partial or center weighted metering mode.</p>

<p>Glad to know this thread is helping people. :)</p>

<p>Last note of caution: I am sure I wrote the direction of turning the potentiometers for larger deflection. So give a try to see which one works. I think is should be CCW for larger deflection.</p>

<p>Good luck.</p>

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